1. Field of the Invention
The present invention relates to an optical multifocal lens having at least two focal points and a method of making the same.
2. Related Background Art
Conventionally known as an optical lens having a plurality of focal points are those shown in FIGS. 5 and 6. In the lens A shown in FIG. 5, a part of one optical surface B is provided with an area having a different curvature. A mold conforming to such an optical surface is employed to integrally mold and make the lens A by glass molding. In the lens D shown in FIG. 6, on the other hand, a UV-curing plastic or the like is attached to one optical surface F of a normal lens E so as to form a surface G having a different curvature. Since a part of the optical surface is provided with an area having a different curvature (C, G), the lenses A and D each function as a bifocal lens which is capable of converging transmitted light at two different points on its optical axis.
Also known is an example employing a Fresnel lens such as that disclosed in Japanese Patent Application Laid-Open No. 8-315402. As shown in FIG. 7, this lens H is formed by a combination of concentric annular bands constituting a longer-focus Fresnel lens I and a shorter-focus Fresnel lens J. As a consequence, light can be converged at two points, i.e., a shorter focal point K and a longer focal point L.